Plasma Etching of silicon dioxide residues in CVD reactors is dominated by fluorine ions and free radicals (F neutrals). CF neutral radicals can also enhance etching of oxide residues but their effect is an order of magnitude less. As SiO.sub.2 is etched, SiF.sub.3 and SiF.sub.4 gas molecules are produced at the SiO.sub.2 surface. These silicon containing gasses leave the SiO.sub.2 surface and are pumped out of the system. Higher overall gas flows and lower reactor pressures assist in this etching process by aiding in the removal of these gasses. In addition, free fluorine production in a PFC plasma is directly related to the presence of oxygen in the glow discharge. Carbon in the PFC gas species is oxidized to form CO or CO.sub.2. Etch rate data for CF.sub.4 plasmas indicate that 12-16 atomic % of oxygen is required to achieve maximum SiO.sub.2 oxide removal rates (C.sub.2 F.sub.6 plasmas required about 30-50% oxygen). Oxygen deficient PFC plasmas tend to generate polymeric residues on the surfaces of components inside the reactor. SiO.sub.2 etching rates decline rapidly on components covered with these polymeric residues (eventually the SiO.sub.2 etching rate will be dominated by the ashing rate of the oxygen neutrals in the plasma, not the ability of the fluorine neutrals to attack the SiO.sub.2). Conversely, if the oxygen concentration in the plasma is increased too much, the plasma will become diluted (the relative fluorine content will drop), therefore SiO.sub.2 residue etch rates will decrease. Addition of hydrogen to PFC/O.sub.2 plasmas reduces SiO.sub.2 residue etch rates by tying up free fluorine radicals in the form of HF vapor. An artifact of this hydrogen effect is to increase the relative carbon to fluorine ratio of the discharge, therefore enhancing polymer generation. As more and more hydrogen is added to the reactor cleaning plasma, polymer production increases (20 atomic % hydrogen in a CF.sub.4 /O.sub.2 plasma will stop oxide etching) and eventually the SiO.sub.2 etch rate is reduced to zero.
Concurrently, CF.sub.4 /O.sub.2, CF.sub.4 /N.sub.2 O, C.sub.2 F.sub.6 /O.sub.2, and NF.sub.3,/AR plasmas are used for PECVD oxide, nitride, and thermal tungsten thin film reactor cleaning. These gasses are presently on the EPA's list of controlled green house gasses (they are subject to strong controls in the near future). However C.sub.2 F.sub.5 H and CF.sub.3 H are not considered controlled green house gasses by the EPA since they lack the chemical stability of their PFC counterparts (they are unable to reach the upper atmosphere and remain there long enough to damage the ozone layer). Reactor cleaning with these hydrogen containing gases is slower due to increased polymerization. In order to compensate for polymerization when using these gasses in reactor cleaning plasmas, additional oxygen must be added to the plasma (this also dilutes the plasma). In order to improve the cleaning rates of C.sub.2 F.sub.5 H and CF.sub.3 H one needs to increase the fluorine radical concentration in the discharge without increasing the flow rate of the hydrogenated PFC gas to increase the efficiency of the plasma in its ability to generate fluorine radicals. In addition, heating the process gas upstream of the chamber could also increase the etching rate of residue of films in the reactor. This is illustrated by the following equation from Lieberman, M. A. and Lichtenberg, A. J. Principles of Plasma Discharges and Materials Processing, John Wiley and Sons, Pub. 1994.: EQU E.sub.r SiO.sub.2 (.ANG./min)=0.61.times.10.sup.-12.eta..sub.fs T.sup.1/2 e.sup.-1892/T
Where E.sub.r SiO.sub.2 is the oxide residue etch rate, .eta..sub.fs is the fluorine radical concentration, and T is the surface reaction temperature in Kelvins.